Along with the performance enhancement of the recent electronic devices such as downsizing and digitalization in higher frequency, there has been growing demand for electronic components, particularly on capacitors, having higher capacitance, low ESR (equivalent series resistance) in a high-frequency region and low leakage current.
Since the capacitance is proportional to the relative dielectric constant and inversely proportional to the thickness of the dielectric layer, it has been demanded to uniformly form a thin dielectric layer having high relative dielectric constant.
With respect to a film formation method of a dielectric layer, there are a dry forming method and a wet forming method. A dry film-forming method includes a film-forming method such as sputtering, a CVD method and vacuum evaporation. In a dry film-forming method, there is a concern of high facility and equipment costs to maintain high-vacuum state, to introduce expensive film-formation equipment, etc. Also, it is difficult to form a film uniformly on a porous substance having a complicated shape due to the presence of concavity and convexity, and therefore the difficulties in controlling the thickness and composition of the film are often pointed out.
As wet film-forming methods, Japanese Patent Application Laid-Open No. S60-116119 (Patent Document 1) and No. S61-30678 (Patent Document 2) disclose technique for forming a thin film of barium titanate by chemically forming a metal titanium substrate in a strong alkali solution containing barium ions. Japanese Patent Application Laid-Open No. H05-124817 (Patent Document 3: related application: U.S. Pat. No. 5,328,718) discloses a technique for forming a thin film of barium titanate on a substrate by alkoxide method.
Japanese Patent Application Laid-Open No. 2003-206135 (Patent Document 4: related application: EP 1445348) discloses a technique for forming a composite titanium oxide film, in which a metal titanium substrate is treated in an aqueous solution of alkali metal to thereby form a titanate of alkali metal on the substrate surface and is further treated in an aqueous solution containing metal ions such as ions of strontium and calcium to thereby substitute the alkali metal with metals such as strontium and calcium. Further, Japanese Patent Application Laid-Open No. H11-172489 (Patent Document 5) discloses a method for producing a barium titanate film by forming a titanium oxide film on a substrate by electrochemical approach and then subjecting the film to anodic oxidation in a barium aqueous solution.
[Patent Document 1]
Japanese Patent Application Laid-Open No. S60-116119
[Patent Document 2]
Japanese Patent Application Laid-Open No. S61-30678
[Patent Document 3]
Japanese Patent Application Laid-Open No. H05-124817
[Patent Document 4]
Japanese Patent Application Laid-Open No. 2003-206135
[Patent Document 5]
Japanese Patent Application Laid-Open No. H11-172489